烟酸二聚体的结构与性质

用密度泛函理论B3LYP方法选取6-311+G(d,p)基组对烟酸-烟酸复合物进行了量子化学计算研究, 通过在相同水平下的频率振动分析发现了势能面上存在7个极小值点, 其最稳定构型1对应一N…H—O型强氢键, 其结合能在消除基组重叠误差后为-48.3 kJ·mol-1. 通过自然键轨道(NBO)分析, 研究了电荷转移及轨道相互作用. 通过自洽反应场(SCRF)理论中的极化连续模型(PCM)在介电常数分别为1.0(真空)、2.247(苯)、10.36(二氯乙烷)、20.7(丙酮)、32.63(甲醇)、78.39(水)的不同溶剂环境下重新优化烟酸复合物势能面上最稳定构型1, 研究了溶剂对烟酸复合物几何构型及结合能的影响. 发现溶剂化作用增大了烟酸复合物分子间的结合能, 导致N…H距离减小. 当溶液介电常数在1.0-32.63范围时, 溶剂效应十分显著, 当介电常数大于32.63后, 溶剂化作用趋于稳定.

Structures and Properties of Nicotinic cid Dimer

Nicotinic acid dimer was subjected to density functional theory calculations using B3LYP/6-311+G(d,p) basis set. Seven equilibrium isomers were located on the potential energy surface. The most stable structure isomer 1 has a strong N…H—O hydrogen-bonding interaction, and its calculated binding energy is -48.3 kJ·mol-1 corrected with basis set superposition error (BSSE).Anormal-mode analysis of the vibrations of the seven isomers was carried out. The charge transfer (CT) and their corresponding second-order interaction energies were studied by nature bond orbital (NBO) analysis. The solvent effects on the geometry of the stablest equilibrium isomer 1 were systematically studied by self-consistent reaction field polarized continuum model (PCM) technique with different dielectric constants of 1.0 (vacuum), 2.247(benzene), 10.36(dichloroethane), 20.7(acetone), 32.63(methanol), and 78.39(water). It was found that the solvent effect would significantly enhance the strength of hydrogen bond as shown by the decrease of the N…H distance. The solvent effect is obvious when ε is in 1.0-32.63 and is weak when ε exceeds 32.63.